356 THE BIOLOGY OF THE PLANT 



on the stem, that the latter is moving ? How 

 long does it continue ? In what part of the 

 stem does the bending begin? Reverse the 

 plants again. Do they again change their 

 position ? 



2. Heliotropism. — Prepare another set of plants in 



the same manner. When they have become 

 well started, revolve the sponge so as to place 

 on the side towards the centre of the room 

 those plants which were on the side towards the 

 window, and vice versa. Does any change take 

 place in the plants? If so, in what direction 

 do they move ? Do you find this to be a com- 

 mon phenomenon among plants? 



3. Twining. — Raise some morning-glory plants in 



a flower-pot covered by a bell-jar, and when the 

 plants are large enough stick into the soil by 

 the side of each a slender stake about a foot 

 long. Does the plant make use of the stake as 

 a support? How high is the plant before it 

 begins to twine ? Do the plants iegin to twine 

 around the stake without first being put in con- 

 tact with it ? What is the first internode which 

 begins the process ? Do all of the plants turn 

 in the same direction around the support ? 



i. Direct observation of the ascent of water in the stem. 



Select a stem of Tradescantia having several 

 long, straight internodes. Hold the stem under 

 water, as in a wash-bowl, and with a razor di- 

 vide it transversely near the lower end of the 

 straight portion, being careful to keep the cut 

 portion of the apical end under water. Then, 

 still holding the stem under water, cut a piece 



